And, on Thursday, in Casa Grande, Arizona, police opened a homicide investigation after four people were shot dead in what appeared to be a domestic violence incident,

According to the nonprofit Gun Violence Archive, in the first nine months of this year, 11,797 people died in gun-related violence, including the victims of the Las Vegas spree.

More than 500 children under 11 have been killed this year.

In the US, various definitions of "mass shooting" are used. The FBI has jurisdiction for "active shooter" incidents, defined as an individual actively engaged in attempting to kill or killing members of the public. A generally accepted definition of a mass killing is one in which three or more people are killed.

This week, a New York Timeseditorial reported 521 mass shootings - defined in the article as four or more people killed in a single event - since the previous most deadly attack, in Orlando, Florida last year, when a gunman opened fire in a nightclub, killing 49 people.